The present invention relates generally to a full time four-wheel drive system and, more particularly, to a full time four-wheel drive system including a torque distribution subassembly which provides automatic torque balancing, differentiation and speed ratioing functions.
Four-wheel drive systems for vehicles are being utilized to a greater extent, providing increased traction and safety of operation for the vehicle. Recently "full time" four-wheel drive systems have been developed for vehicles, wherein a transfer case is typically provided with an interaxle differential for dividing torque between the vehicle front and rear axle differentials. The torque transfer mechanisms to supply drive power to the four wheels of the vehicle are usually connected to a conventional vehicle transmission which is driven by the vehicle engine. As known in the art, conventional transmissions are typically complex in nature and expensive to manufacture due to the quantity and nature of the parts comprising the transmission. For instance, a conventional "automatic" transmission may typically include a plurality of hydraulically actuated multi-disc clutches, a plurality of shifting collars, and a plurality of planetary gear sets, wherein the planetary gear sets are particularly expensive to manufacture.
More recently, transfer case assemblies such as those disclosed in the commonly assigned copending application Ser. No. 07/997,859 have been developed which provide improved torque balancing and differentiation along with the ability to provide extra torque in the event of single wheel or single axle traction loss for improved mobility and stability in a full time four-wheel drive system associated with a vehicle. The transfer case assembly includes an input shaft receiving output torque from a conventional transmission and further includes a continuously variable drive belt connecting the input shaft to one of the output shafts of the transfer case assembly. Notwithstanding the advantages of these systems, automotive design engineers are continually seeking to simplify, and consequently reduce the cost of, vehicle drive train systems and to enhance the driveability of four-wheel drive vehicles.